Description
For whatever reason, when switching to gnuplot-mode for a file, there's absolutely no syntax highlighting whatsoever. I initially thought the mode just didn't come with it, but I found that typing M-x font-lock-mode would bring it up. I don't see a setting for it in gnuplot-mode's customization options, so clearly there's some sort of bug here. Every other major mode enables font lock automatically, there's no reason why this one shouldn't.
I'm no elisp expert, but I'm guessing the fact that the gnuplot-mode function is defined entirely manually (as opposed to deriving from another mode as is typical) means it's missing some code for enabling font lock that you'd usually have done for you via derivation. I can't easily find a description of what a totally manual major mode needs to do, or I'd be able to provide a PR for the issue.